Because what other new-to-expansion race could the Alliance possibly get? Blizzard didn't bother to add anything interesting and worthwhile into Kul Tiras that could possibly end up an Allied Race.

Along those lines. Blizzard went out of their way to withhold any interaction between Vulpera and Alliance. Outside of hostile pirates, we interact with one, and she's a neutral pet battle NPC. Alliance has zero positive interactions with them otherwise.

Also, it seems like Blzzard went out of their way to have Alliance have good relations with the leader of the Devoted Sethrak during the Alliance War Campaign. Like, we have no idea what's going on in Vol'dun. But the one thing we do is save Vorrik's life and take back the Temple of the Devoted before any Horde show up. Then watch the Vampire elf drink a Gnome.